I recently purchased this 94 854T with 144K. It frequently gives off a strong gasoline/exhaust odor that emanates from the engine bay, but quickly work its way in the cabin and seems worse when the heat/AC is on. I've checked fuel lines and exhaust system for obvious leaks/bad fittings, but can't seem to find the source.

Also, there is a hollow knocking sound coming from under the air cleaner box. It starts a few minutes after the engine is started, but matches engine speed/timing.

I'm familiar with the fuel vapor canisters on the 7/940Ts that I've owned - is the 850 counterpart a mechanical unit that is buried under the air cleaner box and could it be the source of the gasoline odor?

Thanks!